1. Field of the Disclosure
The disclosure relates to a light emitting unit array and display device, and particularly, to a micro-light emitting diode array (μ-LED array) and a projection system using the μ-LED array as the projection imaging source.
2. Description of Related Art
LED has the characteristics of high efficiency, long lifespan, etc. and thus the LED light source has been widely applied. The application of the LED in the micro-projection system facilitates a dramatic revolution of the projection and display products. The micro-projection system can be categorized into stand alone type and buried type. The buried type micro-projection system is achieved by burying the micro-projection system in the already existed devices such as the cell phone, the digital camera, the handheld game consoles, and the like.
For burying the projection system in the portable electronic products, a problem needs to be overcome is the reduction of the volume of the product. The conventional micro-projection techniques including the digital light processing (DLP), the liquid crystal projector (LCP), and the liquid crystal on silicon (LCOS) projection device require a complex optical engine which includes illumination, imaging, and projection sub-systems. Accordingly, it is difficult for such products to achieve high projection brightness and further have small volume, e.g. a projection system with micro-volume (<3 cc).
For resolving the above problem, a micro-projection system deduced from the μ-LED array light source is provided. The μ-LED array light source is served as the imaging source and thus the micro-projection system using the μ-LED array light source does not require the complex optical engine. Generally, merely the μ-LED array light source arranged with a projection lens is sufficient to form a high efficient and super small projection system which has the volume smaller than 3 cc. As a whole, the projection system mentioned above facilitates the buried type design of the micro-projection system which is not easily achieved by other micro-projection techniques.
FIG. 1 illustrates a projection system using the μ-LED array light source. As shown in FIG. 1, the projection system 100 includes the μ-LED array 110 arranged on the substrate 10, the μ-lens array 120, and the projection lens 130. The μ-LED array 110 is an array structure formed by a plurality of μ-LEDs and each of the μ-LEDs is served as a pixel for displaying an image. The μ-lens array 120 is disposed on the μ-LED array 110 and includes a plurality of μ-lens. Each of the μ-lens corresponds to one pixel (i.e. one μ-LED). The projection lens 130 is disposed on a light path of the light emitted from the μ-LED array 110.
FIG. 2 is a diagram showing the light path of the light emitted from the μ-LED array of the projection system depicted in FIG. 1. FIG. 3 shows the far field intensity distribution of the μ-LED array of the projection system depicted in FIG. 1. Referring to FIG. 2 and FIG. 3 together, the μ-lens array 120 disposed on the μ-LED array 110 renders the light emitted by the μ-LED array 110 being divided into three groups A, B, and C.
When the μ-LED array 110 displays an image, the two neighboring μ-LEDs can emit the light with different brightness and/or colors to display the required displayed image. However, as shown in FIG. 2 and FIG. 3, the light belonging to the group B and group C emitted from each of the μ-LEDs is emitted obliquely so that the light from each μ-LED can be interfered by the light from the neighboring μ-LED, which is called the optical cross talk effect. Herein, the projection system 100 may have poor imaging quality owing to the optical cross talk effect. For example, the contrast of the projected image is reduced and the projection brightness is decreased. In view of the above, it is an important issue to collimate the light emitted from the μ-LED array 110 when the μ-LED array 110 is applied in the projection system.